Within Glee, characters have had to state if they are gay or straight. So far, those characters have been: Brittany, Santana, Karofsky, Sebastian, Kurt, Blaine, Finn, Puck, Sam, Will, Sue, and Beiste. Out of the main students, the only ones which have not outright said an orientation have been Quinn, Rachel, Artie, Mike, and Tina. And with Quinn’s insane and inconsistent characterization anyway, it is much easier for fanon to interpret canonical scenes and then label her gay. Also, Santana went from bisexual one episode (she out right said she is attracted to men and women) and then next episode she is full out gay.
Since Glee writer’s don’t even know their own characters, it’s impossible for fandom to correctly know them as well. So, basically, if people want to claim Quinn as gay because of interpretation of canonical scenes (like I personally do) cool. If not, there are canonical scenes to prove that as well.
Internet is awesome which allows us to do that.
Just spouting random stuff.